A Look Inside A Vintage Aircraft Altimeter

There’s a strange synchronicity in the projects we see here at Hackaday, where different people come up with strikingly similar stuff at nearly the same time. We’re not sure why this is, but it’s easily observable, with this vintage altimeter teardown and repair by our good friend [CuriousMarc] as the latest example.

The altimeter that [Marc] dissects in the video below was made by Kollsman, which is what prompted us to recall this recent project that turned a jet engine tachometer into a CPU utilization gauge. That instrument was also manufactured by Kollsman, but was electrically driven. [Marc]’s project required an all-mechanical altimeter, so he ordered a couple from eBay.

Unfortunately, thanks to rough handling in transit they arrived in less than working condition, necessitating the look inside. For which we’re thankful, of course, because the guts of these aneroid altimeters are quite impressive. The mechanism is all mechanical, with parts that look like something [Click Spring] would make for a fine timepiece. [Marc]’s inspection revealed the problem: a broken pivot screw keeping the expansion and contraction of the aneroid diaphragms from transmitting force to the gear train that moves the needles. The repair was a little improvisational, with 0.5-mm steel balls used to stand in for the borked piece. It may not be flight ready, but it worked well enough to get the instrument back in action.

We suspect that [Marc] won’t be able to leave well enough alone on this one, so we’ll be on the lookout for a proper repair. In the meantime, he’ll be able to use this altimeter in the test setup he’s building to test a Bendix air data computer from a 1950s-era jet fighter.

21 thoughts on “A Look Inside A Vintage Aircraft Altimeter

  1. Please be *VERY* careful with old aircraft instruments, some of them have Radium markings for the digits and the pointers, which gives off Radon gas, which decays into solid radioactive elements which can lodge in the lungs and cause cancer. Certainly, never suck on the intake tube to move the pointers (as I did when I was a child) and work outside, or in a very well ventilated space. The one I possess, which still glows in the dark, is now sealed in a biscuit tin with hazard warnings on it.

    1. So your uncontrollable fear of things people wouldn’t have batted an eyelash over 40 years ago caused you to relegate one of your childhood hobbies to its eternal tomb inside of a biscuit tin? Despite you having obviously survived childhood with no related issues?


      1. You could scrape a bunch of Radium off those old gauges and snort it through a rolled up $20 (just going with an 80’s vibe for effect) and you would easily survive childhood.

        Bring it forward 40 years to today and you have a good chance having lots of problems. Here are some of the nice ones; Anemia, cataracts, broken teeth and excess cavities. One the nastier end of the scale is Lung, Liver, Bone and Breast Cancer.

        A good, partial definition of the past is “That time when we did a ton of stupid stuff because we didn’t know better.”

        I like playing with all kinds of crazy electronics and chemicals, but I am also very aware of risks and take lots of safety precautions. Mainly because I want to do my fun crazy things for a long time into the future. Hopefully along with my daughter if she continues to like doing stuff with Dad.

        Safety isn’t weakness, and stupidity isn’t bravery. Don’t mistake those. It just makes you sound like my uncle who declared “Smoking hasn’t hurt me for 30 years, why stop?” then died of particularly nasty lung cancer a couple years later.

        1. It’s like one of my university teachers told us, if someone is careful with safety then they will generally be careful and professional with their work too, if they are sloppy with safety then their work will be sloppy too.

          It’s all about doing stuff the right way, someone who does everything properly, including safety, will generally be better than someone that won’t even do it properly for the sake of their own health due to being lazy.

    2. I have red story of one power plant that was testing visitors for radiation before and after visit. Once visitor was above the acceptable levels on entrance – it appeared he found one of those and tried to dismantle.

  2. I have an altimeter, I think it was manufactured in the 1950’s. It has sat on shelves in unheated lean-to sheds, been knocked about and abused with a vacuum cleaner, had the hundred’s hand re-attached by unqualified hands, etc.

    It is still sensitive enough to spot pressure difference in the height of one flight of stairs.

      1. MEMS barometers are advertised as being down to around 10 cm relative altitude accuracy, however noise can affect that. They are commonly used on drones for altitude hold and manage to be pretty stable.

  3. I couldn’t help noticing he installed the inner assembly with the diaphragms 90 degrees counterclockwise from where it was originally. May not be an issue, but it would bother me no end.

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